Particularly in a robotics application, a rotary indexing table may be employed to move a workpiece between two or more index stations or indexing positions. A typical application might be, for example, a two-position indexing table where, at a first position, a workpiece is loaded and clamped onto the table, and at the second position the workpiece is worked on such as by having another element welded onto it in an accurately positioned manner. The indexing table then returns to the first position, where the first workpiece is removed and a second workpiece is placed on the table. Clearly, such operations are capable of being highly automated, but the automation is contingent upon the workpiece being accurately in place at all times. This requirement, in turn, leads to the necessity for rotary indexing tables to have very high degrees of repeatability as they move from one indexing position to the next.
Indeed, typical robotics used in manufacturing processes may require positioning of a workpiece with an accuracy in the order of tenths of a millimeter.
Still further, indexing tables should be capable of moving from one indexing position to the next quite rapidly. The time taken for moving a workpiece from one indexing position to another is non-productive time. However, the action of moving a workpiece from one station to another, by rotating a rotary indexing table from one indexing position to the next, must not be jerky in any manner. In other words, the motion from one indexing position to the next must require a smooth acceleration and deceleration, but as quickly as possible.
Typically, rotary indexing tables will have only two or three indexing positions, but the present invention contemplates that a rotary indexing table may have more indexing positions, because the precise number of indexing positions is immaterial to the invention.
However, typically a rotary indexing table will have two indexing positions, and the motion of the rotary indexing table is reciprocal. That is, the indexing table will rotate clockwise when moving from the first rotary indexing position to the second rotary indexing position, and counterclockwise when returning from the second indexing position to the first indexing position, or vice versa. Such motion permits the wiring, welding leads, compressed air lines, and the like for any robotics equipment which is mounted on the rotary indexing table to move between the first and second indexing positions without becoming unduly tangled.
Another matter of concern, particularly with indexing tables which employ a reciprocating motion, is the matter of backlash. Typically, as intermeshed gears change the direction of relative rotation one with respect to the other, there will be backlash as the mating sides of the intermeshed gears are replaced by the opposite sides of the respective gear teeth; the clearance between the gear teeth of intermeshed gears being required so as to preclude binding and undue wear. As will be noted hereafter, the problem of backlash is overcome by the present invention.
A further problem with rotary indexing tables is the manner in which they are locked in place as they attain and stop their respective indexing positions. Often times, external brakes are required for those purposes; but there is no necessity for any external braking devices in keeping with the present invention, as will be noted hereafter.